Help with math!

Tanya167, LPN · Feb 9, 2018

Oh and this one. Thank you.

Client has an IV of 1,000 ml of D5W, infusing at the rate of 28 gtt/min. The drop factor is 10 gtt/ml. How many milliliter per hour is client receiving?

KrCmommy522, BSN, RN · Feb 9, 2018

Could you show where your at with the problem and hopefully I can help you get to the answer!

When I first learned how to do dosage calculation problems, our instructor showed us all the different equations - dimensional analysis, formula method, ratio proportion - and we got to choose which one we liked best to use. We didn't have to use a specific one. I love dimensional analysis. You just follow it along from what is ordered, canceling out what you don't need, to eventually get to what you have on hand. It just made it easier for me to follow it along that path. You might want to try googling dimensional analysis drops/min calculations and you will see how to go about solving it.

Since the order is mg/kg, you don't have to convert the pts weight.

So you have mg/kg/hr and you need to get gtt/min.

Start with the pts weight (I always start with whatever is in the problem that is on its own, but you could start with the order if that's easier for you). You want gtt/min. So you know that as you follow along your path of dimensional analysis, you eventually want to be left with gtt in a numerator, and min in a denominator.

Now, an important thing to know is that you can only cancel diagonally. So, you have kg in the numerator, to cancel out the kg, the next fraction needs to have kg in the denominator. What in the question has kg? You will use that to cancel out the kgs.

After cancelling out the kg. You go to what is in the numerator of the fraction you used to cancel out the kg. What is in the numerator of that fraction? What is in your problem that you can use to cancel it out? You should use the order of 4 mg/kg/hr to cancel out the kg. So, mg is in the numerator. What is in your problem that you can use to cancel out the mg?

Go from there and let me know if you need any help!

Tanya167, LPN · Feb 9, 2018

Thank you but I'm going to have to sit down and pick apart your answer. We just started learning the math and the teacher is showing us the formula method...

chare · Feb 9, 2018

Why don't you show us which formula your instructor provided? This will better allo us to help you.

KrCmommy522, BSN, RN · Feb 9, 2018

Okay...well as much as I love dimensional analysis...I will help with the formula LoL

Formula For gtt/min = mL/hr x drop factor/60 min = gtt/min

So, you have to calculate mL/hr

4 mg/kg/hr is ordered, multiply that by the pts weight (25 kg) to get mg/hr

Multiply the mg/hr you just got by the 500 mL/1000 mg to get mL/hr.

Substitute the mL/hr in the formula

Tanya167, LPN · Feb 10, 2018

Thank you so much! I really appreciate it.

OsceanSN2018 · Feb 10, 2018

I would set this up with dimensional analysis. I find this formatting to be most helpful because it its easy to see what you do and dont need and cancel things out. And I say this because we haven't learn gtts/min in nursing school yet either, but with simple dimensional analysis I was able to figure it out.

15gtts/1ml x 500ml/1000mg x 4mg/1 kg x 25kg/1 hr x 1hr/60 min

try the next problem on your own and just post it here so we can help you. Also tell me what you don't understand about dimensional analysis.

new gal · Feb 10, 2018

Hello. Very confused. I'm in an LPN program. Some of the math I get and some I'm comfused. Can someone do this problem? Teacher wanted us to try even though she did get to this yet.
client is to receive an IV infusion of 500 ml of D5W with 1000 mg of medication. The drop factor is 15 gtt/ml. The dosage of medication ordered is 4 mg/kg/hr. The client weighs 25 kg. Calculate the flow rate in drops per minute.
please help.
Thank you

12.5 gtts/min

new gal · Feb 10, 2018

Oh and this one. Thank you.
Client has an IV of 1,000 ml of D5W, infusing at the rate of 28 gtt/min. The drop factor is 10 gtt/ml. How many milliliter per hour is client receiving?

168 ml/hr

Tanya167, LPN · Feb 10, 2018

Thank you everyone. Hopefully we will be going over these in class this week. Our teacher just took over the class and she seems a lil all over the place but hopefully things will work out.

bjwojcik · Feb 10, 2018

I have to get my 2 cents in on this one. I also saved it as a pdf, which is easier to follow.

I think it helps to see the big picture on these problems.

You are starting with a rate of 4 mg/kg/h and have to change that to gtts/min.

You are given the patient's weight along with several ratios which you will use to change the units of the given into the units of the answer.

This is how I did it.

Start by setting up the problem with the starting and ending rates. Note that 4 mg/kg/h is mathematically equivalent to 4 mg/kg*h.

(4 mg)/(kg h)= gtt/min

You can now see that you have to change mg to gtts, hours to minutes, and get rid of kg.

Right off the bat you can eliminate kg by inserting the patient's weight into the equation. You will change h to min by using the conversion factor of 1 h/60 min.

(4 mg)/(kg h ) ((25 kg)/)((1 h)/(60 min))= gtt/min

Now you are at mg/min, getting close. You just have to change mg to gtts. You know that there are 1000 mg/500 mL, so that ratio will be used to change mg to mL. There are 15 gtt/mL, so that ratio will change mL to gtts.

(4 mg)/(kg h ) ((25 kg)/)((1 h)/(60 min))((500 mL)/(1000 mg))((15 gtts)/mL)= gtt/min

Now you check everything over making sure the unwanted units are toast and you end up with the desired units.

Do the calculations and you end up with 12.5 gtts/min which would be rounded to 13 gtts/min.

Brad Wojcik, PharmD

IV problem.pdf